Solid electrolyte battery

ABSTRACT

A solid electrolyte battery is disclosed which is capable of raising an energy density without deterioration of discharge load characteristics thereof, incorporating a wound electrode incorporating a positive electrode incorporating an elongated positive-electrode collector having two sides on which positive-electrode active material layers are formed, a negative electrode incorporating an elongated negative-electrode collector having two sides on which negative-electrode active material layers are formed and a solid electrolyte layer formed between the positive electrode and the negative electrode such that the positive electrode and the negative electrode are laminated and wound, wherein when an assumption is made that the total thickness of a pair of the positive-electrode active material layers formed on the two sides of the collector for the positive electrode is total film thickness A and the total thickness of a pair of the negative-electrode active material layers formed on the two sides of the collector for the negative electrode is total thickness B, the total film thickness A of the positive-electrode active material layers satisfies a range from 60 μm to 150 μm, and ratio A/B of the total film thickness A of the positive-electrode active material layers with respect to the total thickness B of the negative-electrode active material layers satisfies a range from 0.5 to 1.2.

RELATED APPLICATION DATA

The present application claims priority to Japanese Application No.P10-295778 filed Oct. 16, 1998 which application is incorporated hereinby reference to the extent permitted by law.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid electrolyte batteryincorporating a solid electrolyte or a gel electrolyte.

2. Description of the Related Art

In recent years, the performance of electronic apparatuses representedby video cameras and portable telephones has significantly been improvedand the sizes of the same have considerably been reduced. Also sizereduction and improvement in the performance of secondary batteriesserving as power sources for the electronic apparatuses have beenrequired. Hitherto, lead batteries and nickel-cadmium batteries havebeen employed as the secondary batteries. Moreover, research anddevelopment of new nonaqueous-electrolyte secondary batteries haveenergetically been performed each of which contains lithium or a lithiumalloy as an active material of a negative electrode.

The nonaqueous-electrolyte secondary battery containing lithium or thelithium alloy as the active material of the negative electrode exhibitsa high energy density. The foregoing nonaqueous-electrolyte secondarybattery suffers from a problem in that the performance deterioratesowing to growth of dendrite and undesirable shortening of the lifetimeagainst charge and discharge cycles. A nonaqueous-electrolyte secondarybattery contains, as the active material of the negative electrode, amaterial, such as a substance, which is able to dope/dedope lithiumions. Moreover, the nonaqueous-electrolyte secondary battery contains,as the active material of the positive electrode, a composite lithiumoxide, such as lithium-cobalt oxide or lithium-nickel oxide. Thenonaqueous-electrolyte secondary battery having the above-mentionedstructure is free from deposition and dissolution reactions of lithiumwhen the reactions of the electrodes are performed. Therefore, thenonaqueous-electrolyte secondary battery exhibits excellent lifetimeagainst charge/discharge cycles.

Recently, a so-called solid electrolyte battery has been suggested asthe nonaqueous-electrolyte secondary battery which contains a carbonmaterial or graphite to constitute the negative electrode. The solidelectrolyte battery contains a solid electrolyte or a gel electrolyte.Among the solid electrolyte batteries, a solid electrolyte battery of atype containing a gel electrolyte obtained by plasticizing a polymermaterial with nonaqueous electrolyte solution exhibits high ionconductivity at room temperatures. Therefore, the above-mentionedsecondary batteries have been expected as promising secondary batteries.

The foregoing solid electrolyte battery is free from apprehension ofleakage of solution and a necessity for providing a sealing structureusing an outer can which has been required for the conventionalstructure. Therefore, the battery can be manufactured by encapsulating awinding-type electrode consisting of a positive electrode and a negativeelectrode with a moistureproof laminated film. Therefore, the solidelectrolyte battery permits reduction in the weight and thickness ascompared with the conventional structure. As a result, the energydensity of the battery can furthermore be improved.

The solid electrolyte battery of the foregoing type suffers from aproblem in that the discharge load characteristics is inferior to thoseof the nonaqueous-electrolyte secondary battery because the ionconductivity of the gel electrolyte is half of the ion conductivity ofthe nonaquaous electrolyte.

SUMMARY OF THE INVENTION

To overcome the foregoing problems experienced with the conventionaltechniques, an object of the present invention is to provide a solidelectrolyte battery which does not deteriorate discharge loadcharacteristics thereof and which is able to raise the energy density.

To achieve the foregoing object, according to one aspect of the presentinvention, there is provided a solid electrolyte battery comprising: awound electrode incorporating a positive electrode incorporating anelongated positive-electrode collector having two sides on whichpositive-electrode active material layers are formed, a negativeelectrode incorporating an elongated negative-electrode collector havingtwo sides on which negative-electrode active material layers are formedand a solid electrolyte layer formed between the positive electrode andthe negative electrode such that the positive electrode and the negativeelectrode are laminated and wound, wherein when an assumption is madethat the total thickness of a pair of the positive-electrode activematerial layers formed on the two sides of the collector for thepositive electrode is total film thickness A and the total thickness ofa pair of the negative-electrode active material layers formed on thetwo sides of the collector for the negative electrode is total thicknessB, the total film thickness A of the positive-electrode active materiallayers satisfies a range from 60 μm to 150 μm, and ratio A/B of thetotal film thickness A of the positive-electrode active material layerswith respect to the total thickness B of the negative-electrode activematerial layers satisfies a range from 0.5 to 1.2.

Since the solid electrolyte battery according to the present inventionis structured as described above, the energy density of the battery canbe raised without deterioration in the discharge load characteristics ofthe battery when an optimum value of the thickness ratio A/B of thetotal film thickness A of the negative-electrode active material layerswith respect to the total thickness B of the negative-electrode activematerial layers is obtained.

Other objects, features and advantages of the invention will be evidentfrom the following detailed description of the preferred embodimentsdescribed in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing the structure of apolymer lithium-ion secondary battery according to an embodiment of thepresent invention;

FIG. 2 is a perspective view showing the structure of the polymerlithium ion secondary battery;

FIG. 3 is a diagram schematically showing the structure of awinding-type electrode of the polymer lithium-ion secondary battery;

FIG. 4 is a vertical cross sectional view showing the structure of apositive electrode of the polymer lithium-ion secondary battery;

FIG. 5 is a vertical cross sectional view showing a gel electrolytelayer formed on the positive electrode of the polymer lithium-ionsecondary battery;

FIG. 6 is a plan view showing the structure of the positive electrode ofthe polymer lithium-ion secondary battery;

FIG. 7 is a vertical cross sectional view showing the structure of anegative electrode of the polymer lithium-ion secondary battery;

FIG. 8 is a vertical cross sectional view showing a gel electrolytelayer formed on the negative electrode of the polymer lithium-ionsecondary battery;

FIG. 9 is a plan view showing the structure of the negative electrode ofthe polymer lithium-ion secondary battery;

FIG. 10 is a cross sectional view showing an essential portion of thestructure of a laminated film of the polymer lithium-ion secondarybattery;

FIG. 11 is a side view viewed from an arrow C shown in FIG. 2 andshowing an essential portion;

FIG. 12 is a graph showing the relationship between thickness ratios andcapacity ratios; and

FIG. 13 is a graph showing the relationship between thickness ratios andenergy densities.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will now be described withreference to the drawings. Referring to FIGS. 1 and 2, the structure ofthe polymer lithium-ion secondary battery 1 according to the embodimentof the present invention will now be described. A positive-electrodelead wire 3 and a negative-electrode lead wire 4 connected to a woundelectrode 2 and serving as external terminals are drawn out to theoutside portion. The wound electrode 2 is encapsulated by an upperlaminated film 6 and a lower laminated film 7 which constitute a casemember 5.

As shown in FIG. 3, the wound electrode 2 is structured such that apositive electrode 8 and a negative electrode 9 are laminated and woundthrough a separator 10. A gel electrolyte layer 11 is formed between thepositive electrode 8 and the separator 10 and between the negativeelectrode 9 and the separator 10.

As shown in FIG. 4, the positive electrode 8 is constituted by forming apositive-electrode active material layer 13 on each of the two sides ofa positive-electrode collector 12. Moreover, the positive electrode 8has a gel electrolyte layer 11 formed on each of the positive-electrodeactive material layers 13 formed on the two sides thereof, as shown inFIG. 5.

As shown in FIGS. 4 and 5, an assumption about the positive electrode 8is made that the thicknesses of the positive-electrode active materiallayers 13 formed on the two sides of the positive-electrode collector 12are A₁ and A₂. Another assumption is made that the total thickness ofthe pair of the positive-electrode active material layers 13 is A.Therefore, the total film thickness A of the positive-electrode activematerial layers 13 can be obtained by calculating A₁+A₂.

The positive-electrode collector 12 may be constituted by metal foil,such as aluminum foil, nickel foil or stainless steel foil. It ispreferable that the foregoing metal foil is porous metal foil. When theporous metal foil is employed, the adhesive strength between thecollector and the electrode layers can be raised. The porous metal foilmay be punching metal, expand metal or metal foil having a multiplicityof openings formed by performing an etching process.

The positive-electrode active material for constituting thepositive-electrode active material layers 13 may be metal oxide, metalsulfide or a specific polymer material.

The positive-electrode active material may be Li_(x)MO₂(where M is oneor more types of transition metal, preferably Co, Ni or Mn and x whichvaries depending on the state of charge/discharge of the batterysatisfies 0.05<×<1.12). It is preferable that the transition metalconstituting the composite lithium oxide is Co, Ni or Mn. The compositelithium oxide is exemplified by LiCoO₂, LiNiO₂, LiNi_(y)Co_(1−y)O₂(where 0<y<1) and LiMn₂O₄.

Two or more types of the positive-electrode active materials may bemixed to constitute the positive-electrode active material layers 13.When the positive-electrode active material layers 13 is formed, a knownconducting material and/or a known binder may be added.

As shown in FIG. 6, the positive electrode 8 has alengthwise-directional end at which an exposed portion 12 a is formed inwhich the positive-electrode collector 12 is exposed to correspond tothe width of the positive-electrode lead wire 3. The positive-electrodelead wire 3 is joined to the exposed portion 12 a of thepositive-electrode collector 12 such that the positive-electrode leadwire 3 is drawn out from a widthwise-directional end of the exposedportion 12 a of the positive-electrode collector 12.

As shown in FIG. 7, the negative electrode 9 has negative-electrodeactive material layer 15 formed on each of the two sides of thenegative-electrode collector 14. As shown in FIG. 8, the negativeelectrode 9 incorporates the negative-electrode active material layer 15formed on each of the two sides thereof and having the gel electrolytelayer 11 formed on each of the two sides thereof.

As shown in FIGS. 7 and 8, an assumption about the negative electrode 9is made that the thicknesses of the negative-electrode active materiallayers each of which is formed on each of the two sides of thenegative-electrode collector are B₁ and B₂. Another assumption is madethat the total thickness of the pair of the negative-electrode activematerial layers is B. The total film thickness B of thenegative-electrode active material layers can be obtained by calculatingB₁+B₂.

The negative-electrode collector 14 may be constituted by metal foil,such as copper foil, nickel foil or stainless steel foil. It ispreferable that the metal foil is porous metal foil. Since the porousmetal foil is employed, the adhesive strength between the collector andthe electrode layer can be raised. The porous metal foil may be any oneof punching metal, expand metal and metal foil having a multiplicity ofopenings formed by performing an etching process.

It is preferable that the negative-electrode active material forconstituting the negative-electrode active material layers 15 is amaterial which is capable of doping/dedoping lithium. The materialcapable of doping/dedoping lithium is exemplified by graphite, anon-graphitizable carbon material and a graphitizable carbon material.The carbon material is exemplified by carbon black, such as pyrolysiscarbon or acetylene black, graphite, vitreous carbon, active carbon,carbon fiber, a sintered compact of organic polymer, a sintered compactof coffee beans, a sintered compact of cellulose and a sintered compactof bamboo.

Two or more types of the negative-electrode active materials may bemixed to constitute the negative-electrode active material layers 15.When the negative-electrode active material layers 15 is constituted, aknown conducting material and/or a known binder may be added.

As shown in FIG. 9, the negative electrode 9 has an exposed portion 14 ain which the negative-electrode collector 14 is exposed to correspond tothe width of the negative-electrode lead wire 4, the exposed portion 14a being formed at a lengthwise-directional end of the negative electrode9. A negative-electrode lead wire 4 is joined to the exposed portion 14a in which the negative-electrode collector 14 is exposed in such amanner that the negative-electrode lead wire 4 is drawn out from awidthwise-directional end of exposed portion 14 a.

It is preferable that the separator 10 is constituted by a thin filmhaving small pores and exemplified by polypropylene, polyethylene ortheir composite material. It is furthermore preferable that a thin filmhaving small pores is employed which has improved wettability withrespect to electrolyte solution by using a surface active agent or byperforming a corona discharge process. As a result, rise in theresistance in the battery can be prevented.

When the gel electrolyte layer 11 is formed, a nonaqueous solvent may beemployed which is exemplified by ethylene carbonate, polypropylenecarbonate, butylene carbonate, γ-butyl lactone, γ-valerolactone,diethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, 1,3-dioxane,methyl acetate, methyl propiolic acid, dimethyl carbonate, diethylcarbonate, ethylmethyl carbonate, 2,4-difluoroanisole,2,6-difluoroanisole and 4-bromoveratrole. The foregoing material may beemployed solely or two or more types of the foregoing materials may beemployed as mixed solvent.

When a moistureproof laminated film is employed to constitute the casemember 5, the nonaqueous solvent may be composed of a combination of thefollowing materials having a boiling point of 150° C. or higher andexemplified by ethylene carbonate, polypropylene carbonate, γ-butyllactone, 2,4-difluoroanisole, 2,6-difluoroanisole and 4-bromoveratrole.

When the gel electrolyte layer 11 is formed, an electrolyte salt isemployed which is exemplified by lithium salt, such as LiPF₆, LiAsF₆,LiBF₄, LiClO₄, LiCF₃SO₃, Li(CF₃SO₂)₂N and LiC₄FSO₃. The foregoinglithium salt may be employed solely or two or more types of the lithiumsalts may be combined. It is preferable that the quantity of theelectrolyte salt which must be added is such that the molarconcentration in the nonaqueous electrolyte in the gel electrolyte is0.10 mol/l to 2.0 mol/l in order to realize a satisfactory ionconductivity.

When the gel electrolyte layer 11 is formed, the polymer material forpreparing the gel electrolyte is employed. The polymer material may bepolyvinylidene fluoride or copolymer of polyvinylidene fluoride. Thecopolymer monomer is exemplified by hexafluoropolypropylene andtetrafluoroethylene.

The polymer material for constituting the gel electrolyte may be, forexample, polyacrylonitrile or a copolymer of polyacrylonitrile. Thecopolymer monomer (vinyl monomer) may be any one of the followingmaterials: for example, vinyl acetate, methyl methacrylate, butylmethacrylate, methyl acrylate, butyl acrylate, itaconic acid, methylacrylate hydride, ethylacrylate hydride, acrylamide, vinyl chloride,vinylidene fluoride and vinylidene chloride. As an alternative to this,any one of the following materials may be employed: acrylonitrilebutadiene rubber, acrylonitrile butadiene-styrene resin, acrylonitrilepolyethylene-propylene-dienestyrene chloride resin, acrylonitrile vinylchloride resin, acrylonitrile methaacrylate resin and acrylonitrileacrylate resin.

The polymer material for constituting the gel electrolyte may bepolyethylene oxide or a copolymer of polyethylene oxide. The copolymermonomer may be, for example, polypropylene oxide, methylmethacrylate,butyl methacrylate, methyl acrylate or butyl acrylate.

The polymer material for constituting the gel electrolyte may bepolyether denatured siloxane or its copolymer.

The polymer material for constituting the gel electrolyte may beemployed solely or two or more types of the foregoing materials may bemixed.

To obtain a satisfactory gel electrolyte of the gel electrolyte layer11, it is preferable that the quantity of the polymer material whichmust be added is, for example, about 5% to about 50% with respect to theweight of the electrolyte solution. Although the gel electrolyte isemployed as the solid electrolyte of the gel electrolyte layer 11, anymaterial having an ion conductivity of 1 mS/cm or greater at roomtemperatures may be employed as a substitute for the gel solidelectrolyte. For example, a solid polymer electrolyte may be employedwhich is composed of a polymer material obtained by swelling nonaqueoussolution which contains the foregoing electrolyte salt. The polymermaterial for constituting the solid electrolyte may be, for example,polyethylene oxide, polypropylene oxide, polyphosphagen or polysiloxane.

Although the laminated electrolyte 2 has the structure that theseparator is disposed between the positive electrode 8 and the negativeelectrode 9, the present invention is not limited to the foregoingstructure. A structure may be employed in which a gel electrolyte layer10 is formed between the positive electrode 8 and the negative electrode9 as a substitute for the structure in which the separator is disposedbetween the positive electrode 8 and the negative electrode 9.

The positive-electrode lead wire 3 and the negative-electrode lead wire4 may be made of metal, such as aluminum, copper, nickel or stainlesssteel. Each of the positive-electrode lead wire 3 and thenegative-electrode lead wire 4 is formed into a thin plate-like shape ora mesh shape. The positive-electrode lead wire 3 and thenegative-electrode lead wire 4 are joined to the corresponding exposedportion 12 a of the positive-electrode collector 12 and the exposedportion 14 a of the negative electrode 14 of the negative electrode 9by, for example, resistance welding or supersonic welding.

As shown in FIG. 10, the case member 5 must have moistureproofingcharacteristic. For example, the case member 5 has a three-layerstructure obtained by bonding the nylon film 16, the aluminum foil 17and the polyethylene film 18 in this sequential order. As shown in FIGS.1 and 2, the case member 5 has a projecting structure such that theupper laminated film 6 accommodates the wound electrode 2 and an outerend portion 6 a which must be welded is left.

When the wound electrode 2 is encapsulated in the case member 5, theouter end portion 6 a of the upper laminated film 6 and the lowerlaminated film 7 are welded to each other with heat such that thepolyethylene film of the upper laminated film 6 and that of the lowerlaminated film 7 face inside. Then, the internal pressure is reduced andthe case member 5 is sealed. At this time, the case member 5encapsulates the wound electrode 2 such that the positive-electrode leadwire 3 and the negative-electrode lead wire 4 are drawn out from thecase member 5.

The structure of the case member 5 is not limited to the foregoingstructure. For example, a structure may be employed in which a laminatedfilm formed into a bag shape encapsulates the wound electrode 2. In theforegoing case, the wound electrode 2 is accumulated in the case member5. Then, the pressure in the case member 5 is reduced and the casemember 5 is sealed such that the positive-electrode lead wire 3 and thenegative-electrode lead wire 4 are drawn out to the outside portion.

As shown in FIGS. 1, 2 and 11, when the wound electrode 2 isencapsulated in the case member 5, the upper and lower fusible films 19made of polyolefine resin are placed on the contact portion among thecase member 5, the positive-electrode lead wire 3 and thenegative-electrode lead wire 4 to hold the positive-electrode lead wire3 and the negative-electrode lead wire 4.

The fusible film 19 must have adhesivity with respect to thepositive-electrode lead wire 3 and the negative-electrode lead wire 4.For example, polyolefine resin which is the material of the fusible film19 is exemplified by polyethylene, polypropylene, denaturedpolyethylene, denatured polypropylene and a copolymer of any one of theforegoing materials. It is preferable that the thickness of the fusiblefilm 19 realized before the fusible film 19 is fused with heat satisfies20 μm to 200 μm. If the thickness which is realized before the fusiblefilm 19 is fused is smaller than 20 μm, easy handling is not permitted.If the thickness which is realized before the fusible film 19 is fusedis larger than 200 μm, water easily penetrates the fusible film 19. Inthis case, airtightness in the battery cannot easily be maintained.

Therefore, when the wound electrode 2 is encapsulated in the case member5, the fusible film 19 is welded by performing a heat welding operation.Thus, the adhesiveness among the positive-electrode lead wire 3, thenegative-electrode lead wire 4 and the case member 5 can furthermore beimproved.

The polymer lithium-ion secondary battery 1 according to the presentinvention has the above-mentioned structure which is characterized inthat the total film thickness A of the positive-electrode activematerial layers 13 satisfies the range from 60 μm to 150 μm. Moreover,the ratio A/B of the total film thickness A of the positive-electrodeactive material layers 13 with respect to the total film thickness B ofthe negative-electrode active material layers 15 satisfies the rangefrom 0.5 to 1.2.

The optimum thickness ratio A/B of the total film thickness A of thepositive-electrode active material layers with respect to the total filmthickness B of the negative-electrode active material layer is obtainedas described above. Therefore, the discharge load characteristic of thebattery can be improved. Thus, the energy density of the battery canfurthermore be raised.

When the gel electrolyte of the gel electrolyte layer 11 ispolyvinylidene fluoride, it is preferable that a gel electrolyte isemployed which is composed of multiple polymer obtained bycopolymerizing polyhexafluoropolypropylene or polytetrafluoroethylene.As a result, a gel electrolyte having higher mechanical strength can beobtained.

To raise the mechanical strength of the gel electrolyte layer 11, it ispreferable that a gel electrolyte is employed which is composed ofpolymer obtained by copolymerizing hexafluoropolypropylene at a ratiowhich is lower than 8 wt % with respect to polyvinylidene fluoride. Morepreferably, a gel electrolyte is employed which is composed of polymerobtained by block-copolymerizing hexafluoropolypropylene at a ratio notless than 3 wt % nor more than 7.5 wt %.

The reason why the ratio of the hexafluoropolypropylene is 7.5 wt % orlower lies in that satisfactory strength cannot be realized when theratio is higher than the above-mentioned value. The reason why the ratiois 3 wt % or higher lies in that the effect of improving the solventmaintaining performance by copolymerizing hexafluoropolypropylene cannotsatisfactorily be obtained. In this case, solvent in a sufficientlylarge quantity cannot be maintained.

It is preferable that the total thickness A+B of the total filmthickness A of the positive-electrode active material layer and thetotal film thickness B of the negative-electrode active material layeris 500 μm or smaller, more preferably 300 μm or smaller.

EXAMPLES

Examples of the polymer lithium-ion secondary battery according to thepresent invention will now be described. Moreover, comparative examplesmanufactured to be compared with the examples will now be described.

Example 1

In Example 1, the positive electrode was manufactured by initiallymixing marketed lithium carbonate and cobalt carbonate such that thecomposition ratio of lithium atoms and cobalt atoms was 1:1. Then, themixture was calcinated in air at 900° C. for 5 hours, resulting inobtaining lithium cobalt oxide (LiCoO₂) which was employed as the activematerial of the positive electrode. The lithium cobalt oxide in aquantity of 91 wt %, carbon black serving as a conducting material in aquantity of 6 wt % and polyvinylidene fluoride serving as a binder in aquantity of 3 wt % were mixed so that a mix for constituting thepositive electrode was obtained. The mix for the positive electrode isdispersed in N-methylpyrolidone so that slurry (in the form of paste)was obtained. Then, the obtained mix slurry for the positive electrodewas uniformly applied to the two sides of aluminum foil which was formedinto the collector of the positive electrode and which had a thicknessof 20 μm. Then, the two sides of the aluminum foil were dried, and thena roller pressing machine was operated to compression-mold the aluminumfoil so that an elongated positive electrode was manufactured.

The thicknesses A₁ and A₂ of the positive-electrode active materiallayer formed on each of the two sides of the collector of the positiveelectrode were substantially the same. The total film thickness A of thepair of the active material of the positive electrode was 60 μm. Thedensity of the positive-electrode active material layer was 3.6 g/cm³.

The negative electrode was manufactured such that graphite in a quantityof 90 wt % and polyvinylidene fluoride serving as the binder in aquantity of 10 wt % were mixed so that a mix for the negative electrodewas obtained. The mix for the negative electrode was dispersed inN-methylpyrolidone so that slurry (in the form of paste) was obtained.Then, the obtained mix slurry for the negative electrode was uniformlyapplied to the two sides of copper foil which was formed into thecollector of the negative electrode and which had a thickness of 15 μm.Then, the two sides of the copper foil were dried, and then a rollerpressing machine was operated to compression-mold the copper foil sothat an elongated negative electrode was manufactured.

The thicknesses B₁ and B₂ of the negative-electrode active materiallayer formed on each of the two sides of the collector of the negativeelectrode were substantially the same. The total film thickness B of thepair of the active material of the negative electrode was 50 μm. Thedensity of the negative-electrode active material layer was 1.6 g/cm³.

Therefore, the thickness ratio A/B of the total film thickness A of thepositive-electrode active material layer with respect to the total filmthickness B of the negative-electrode active material layer was 1.20.

The negative-electrode lead wire made of mesh-shape copper wasspot-welded to the negative electrode, while a positive-electrode leadwire made of mesh-shape aluminum was spot-welded to the positiveelectrode. The negative and positive electrode lead wires served asterminals for producing external outputs.

The gel electrode layer was formed by using a polymer material obtainedby block-copolymerizing polyvinylidene fluoride andhexafluoropolypropylene at a weight ratio of 93:7. Initially,2,4-difluoroanisole in a quantity of 1 wt % was added to solutionobtained by mixing dimethylcarbonate in a quantity of 80 parts byweight, γ-butyllactone in quantity of 42 parts by weight, ethylenecarbonate in a quantity of 50 parts by weight propylene carbonate in aquantity of 8 parts by weight and LiPF₆ in a quantity of 18 parts byweight. Then, copolymer of polyvinylidene fluoride andhexafluoropolypropylene in a quantity of 10 wt % was added to theforegoing solution so as to uniformly dispersed by a homogenizer. Then,the solution was heated and stirred at 75° C. After the mixed solutionwas changed to a colorless and transparent state, stirring wasinterrupted. Then, the solution was uniformly applied to the two sidesof each of the positive electrode and the negative electrode by using adoctor blade. Then, the structure was placed in a drying furnace set to70° C. for three minutes so that a gel electrolyte layer having athickness of about 25 μm was formed on the surface of each of thepositive electrode and the negative electrode.

While thus-manufactured negative electrode and the positive electrodewere being laminated, the negative electrode and the positive electrodewere wound many times. Thus, a wound electrode was manufactured. Theobtained wound electrode was encapsulated into a laminated film underreduced pressure while the lead wire of the negative electrode and thelead wire of the positive electrode were being drawn out to the outsideportion. As a result, a polymer lithium-ion secondary battery wasmanufactured.

Examples 2 to 4

Polymer lithium-ion secondary batteries according to Examples 2 to 4were manufactured similarly to Example 1 except for the total filmthickness A of the positive-electrode active material layer which wasidentically 60 μm and the total film thicknesses B of thenegative-electrode active material layer which were as shown in Table 1.In Examples 2 to 4, the thickness ratios A/B of the total film thicknessA of the positive-electrode active material layer with respect to thetotal film thickness B of the negative-electrode active material layerwere made to be 1.00, 0.80 and 0.60 by changing the total film thicknessB of the negative-electrode active material layer.

Examples 5 to 8

Polymer lithium-ion secondary batteries according to Examples 5 to 8were manufactured similarly to Example 1 except for the total filmthickness A of the positive-electrode active material layer which wasidentically 90 μm and the total film thicknesses B of thenegative-electrode active material layer which were as shown in Table 1.In Examples 5 to 8, the thickness ratios A/B of the total film thicknessA of the positive-electrode active material layer with respect to thetotal film thickness B of the negative-electrode active material layerwere made to be 1.00, 0.80 and 0.60 by changing the total film thicknessB of the negative-electrode active material layer.

Examples 9 to 12

Polymer lithium-ion secondary batteries according to Examples 9 to 12were manufactured similarly to Example 1 except for the total filmthickness A of the positive-electrode active material layer which wasidentically 120 μm and the total film thicknesses B of thenegative-electrode active material layer which were as shown in Table 1.In Examples 9 to 12, the thickness ratios A/B of the total filmthickness A of the positive-electrode active material layer with respectto the total film thickness B of the negative-electrode active materiallayer were made to be 1.00, 0.80 and 0.60 by changing the total filmthickness B of the negative-electrode active material layer.

Examples 13 to 16

Polymer lithium-ion secondary batteries according to Examples 13 to 16were manufactured similarly to Example 1 except for the total filmthickness A of the positive-electrode active material layer which wasidentically 150 μm and the total film thicknesses B of thenegative-electrode active material layer which were as shown in Table 1.In Examples 13 to 16, the thickness ratios A/B of the total filmthickness A of the positive-electrode active material layer with respectto the total film thickness B of the negative-electrode active materiallayer were made to be 1.00, 0.80 and 0.60 by changing the total filmthickness B of the negative-electrode active material layer.

Comparative Examples 1 to 3

Polymer lithium-ion secondary batteries according to ComparativeExamples 1 to 3 were manufactured similarly to Example 1 except for thetotal film thickness A of the positive-electrode active material layerwhich was identically 60 μm and the total film thicknesses B of thenegative-electrode active material layer which were as shown in Table 1.In Comparative Examples 1 to 3, the thickness ratios A/B of the totalfilm thickness A of the positive-electrode active material layer withrespect to the total film thickness B of the negative-electrode activematerial layer were made to be 1.40, 0.40 and 0.20 by changing the totalfilm thickness B of the negative-electrode active material layer.

Comparative Examples 4 to 6

Polymer lithium-ion secondary batteries according to ComparativeExamples 4 to 6 were manufactured similarly to Example 1 except for thetotal film thickness A of the positive-electrode active material layerwhich was identically 90 μm and the total film thicknesses B of thenegative-electrode active material layer which were as shown in Table 1.In Comparative Examples 4 to 6, the thickness ratios A/B of the totalfilm thickness A of the positive-electrode active material layer withrespect to the total film thickness B of the negative-electrode activematerial layer were made to be 1.40, 0.40 and 0.20 by changing the totalfilm thickness B of the negative-electrode active material layer.

Comparative Examples 7 to 9

Polymer lithium-ion secondary batteries according to ComparativeExamples 7 to 9 were manufactured similarly to Example 1 except for thetotal film thickness A of the positive-electrode active material layerwhich was identically 120 μm and the total film thicknesses B of thenegative-electrode active material layer which were as shown in Table 1.In Comparative Examples 7 to 9, the thickness ratios A/B of the totalfilm thickness A of the positive-electrode active material layer withrespect to the total film thickness B of the negative-electrode activematerial layer were made to be 1.40, 0.40 and 0.20 by changing the totalfilm thickness B of the negative-electrode active material layer.

Comparative Examples 10 to 12

Polymer lithium-ion secondary batteries according to ComparativeExamples 10 to 12 were manufactured similarly to Example 1 except forthe total film thickness A of the positive-electrode active materiallayer which was identically 150 μm and the total film thicknesses B ofthe negative-electrode active material layer which were as shown inTable 1. In Comparative Examples 10 to 12, the thickness ratios A/B ofthe total film thickness A of the positive-electrode active materiallayer with respect to the total film thickness B of thenegative-electrode active material layer were made to be 1.40, 0.40 and0.20 by changing the total film thickness B of the negative-electrodeactive material layer.

Comparative Examples 13 to 19

Polymer lithium-ion secondary batteries according to ComparativeExamples 13 to 19 were manufactured similarly to Example 1 except forthe total film thickness A of the positive-electrode active materiallayer which was identically 180 μm and the total film thicknesses B ofthe negative-electrode active material layer which were as shown inTable 1. In Comparative Examples 13 to 19, the thickness ratios A/B ofthe total film thickness A of the positive-electrode active materiallayer with respect to the total film thickness B of thenegative-electrode active material layer were made to be 1.40, 1.20,1.00, 0.80, 0.60, 0.40 and 0.20 by changing the total film thickness Bof the negative-electrode active material layer.

TABLE 1 Total Film Total Film Thickness A of Thickness B of PositiveElectrode Negative Film Thickness (μm) Electrode (μm) Ratio A/B Example1 60 50 1.20 Example 2 60 60 1.00 Example 3 60 75 0.80 Example 4 60 1000.60 Example 5 90 75 1.20 Example 6 90 90 1.00 Example 7 90 113 0.80Example 8 90 150 0.60 Example 9 120 100 1.20 Example 10 120 120 1.00Example 11 120 150 0.80 Example 12 120 200 0.60 Example 13 150 125 1.20Example 14 150 150 1.00 Example 15 150 188 0.80 Example 16 150 250 0.60Comparative 60 43 1.40 Example 1 Comparative 60 150 0.40 Example 2Comparative 60 300 0.20 Example 3 Comparative 90 64 1.40 Example 4Comparative 90 225 0.40 Example 5 Comparative 90 450 0.20 Example 6Comparative 120 86 1.40 Example 7 Comparative 120 300 0.40 Example 8Comparative 120 600 0.20 Example 9 Comparative 150 107 1.40 Example 10Comparative 150 375 0.40 Example 11 Comparative 150 750 0.20 Example 12Comparative 180 129 1.40 Example 13 Comparative 180 150 1.20 Example 14Comparative 180 180 1.00 Example 15 Comparative 180 225 0.80 Example 16Comparative 180 300 0.60 Example 17 Comparative 180 450 0.40 Example 18Comparative 180 900 0.20 Example 19 Capacity Ratio Energy Density (%)(Wh/1) Example 1 93 205 Example 2 92 230 Example 3 91 223 Example 4 94217 Example 5 84 215 Example 6 83 242 Example 7 82 234 Example 8 85 228Example 9 75 226 Example 10 75 254 Example 11 74 246 Example 12 76 239Example 13 68 223 Example 14 67 250 Example 15 66 242 Example 16 69 236Comparative 92 192 Example 1 Comparative 92 206 Example 2 Comparative 90198 Example 3 Comparative 83 202 Example 4 Comparative 83 216 Example 5Comparative 81 208 Example 6 Comparative 75 212 Example 7 Comparative 75227 Example 8 Comparative 73 218 Example 9 Comparative 67 209 Example 10Comparative 67 224 Example 11 Comparative 66 215 Example 12 Comparative54 202 Example 13 Comparative 54 216 Example 14 Comparative 54 242Example 15 Comparative 53 235 Example 16 Comparative 55 229 Example 17Comparative 54 217 Example 18 Comparative 52 209 Example 19

Experiments for Evaluating Characteristics

The thus-manufactured polymer lithium-ion secondary batteries accordingto Examples 1 to 16 and Comparative Examples 1 to 19 were subjected tocharging and discharging operation experiments by using apotentiogalvanostat by a constant-current and constant-voltage method.Then, discharge capacities required to obtain capacity ratios and energydensities were measured. The measurement was performed by the followingmethod.

Initially, charging was started with an electric current of 200 mA. Whenthe voltage of a closed circuit was raised to 4.2 V, the charging methodwas changed to constant-voltage. After 8 hours were elapsed from thestart of the experiment, the charging operation was completed. Then,discharge was performed under the constant-current condition of 200 mA.When the voltage of the closed circuit was raised to 3.0 V, thedischarging operation was completed. The foregoing charging/dischargingcycles was performed three times. The discharge capacity obtained afterthe third discharging operation was performed was measured.

Then, charging was started with a current value of 500 mA. When thevoltage of the closed circuit was raised to 4.2 V, the charging methodwas changed to the constant-voltage charging method. The chargingoperation was completed three hours after the start of the experiment.Then, discharge was performed under the constant-current condition of3000 mA. When the voltage of the closed circuit was raised to 3.0 V, thedischarging operation was completed.

The capacity ratio was evaluated by obtaining the discharge capacityrealized at the third cycle and the discharge capacity at the fourthcycle by using the following equation:${CapacityRatio} = {\frac{{discharge}\quad {capacity}\quad {at}\quad {fourth}\quad {cycle}}{{discharge}\quad {capacity}\quad {at}\quad {third}\quad {cycle}} \times 100}$

The energy density was evaluated by obtaining the same in accordancewith the discharge capacity at the third cycle, the average dischargevoltage and the volume of the battery.

Results of the evaluations were shown in Table 1.

In accordance with the obtained results of the evaluations, therelationship between the thickness ratios and the capacity ratiosrealized when the total film thickness A of the positive-electrodeactive material layer was 60 μm, 90 μm, 120 μm and 180 μm as shown inFIG. 12 were obtained so that the evaluation was performed. Similarly,the relationships between the thickness ratios and energy densities asshown in FIG. 13 were obtained so that the evaluation was performed.

As can be understood from FIG. 12, when the cases where the total filmthicknesses A of the positive-electrode active material layer were 60μm, 90 μm, 120 μm and 180 μm were indicated with five curves, thecapacity ratio of each battery was 65% or higher when the total filmthickness A of the positive-electrode active material layer was 150 μmor smaller. When the total film thickness A of the positive-electrodeactive material layer was 60 μm, the capacity ratio of each battery was90% or higher. Therefore, excellent load characteristics were confirmed.

When the total film thickness A of the positive-electrode activematerial layer was 180 μm, the capacity ratio of the battery was about50%. Therefore, a fact was confirmed that a satisfactory capacity ratiowas not obtained as compared with the other batteries.

As can be understood from FIG. 13, when the cases where the total filmthickness A of the positive-electrode active material layer was 60 μm,90 μm, 120 μm, 150 μm and 180 μm were indicated with five curved lines,a fact was confirmed that the energy density was improved as the totalfilm thickness A of the positive-electrode active material layer wasenlarged. When the total film thickness A of the positive-electrodeactive material layer was 180 μm, the energy density was undesirablylowered as compared with the case in which the total film thickness A ofthe positive-electrode active material layer was 150 μm. When the totalfilm thickness A of the positive-electrode active material layer was 60μm, the energy density was 200 Wh/1 or lower depending on the thicknessratio A/B. In the foregoing case, the characteristics required for thebattery from the market cannot be satisfied (Comparative Example 1 inwhich the thickness ratio A/B was 1.40 and Comparative Example 3 inwhich the thickness ratio A/B was 0.20).

As the thickness ratio A/B was raised, the energy density was raised inany case. When the thickness ratio A/B was about 1.00, the energydensity was maximized. If the thickness ratio A/B was furthermoreraised, the energy density was lowered.

Thus, it is preferable that the total film thickness A of thepositive-electrode active material layer satisfies the range from 60 μmto 150 μm. It is preferable that the thickness ratio A/B of the totalfilm thickness A of the positive-electrode active material layer withrespect to the total film thickness B of the negative-electrode activematerial layer satisfies the range from 0.5 to 1.2.

As described above, the present invention is structured such that theoptimum values of the total film thickness A of the positive-electrodeactive material layers of the solid electrolyte battery incorporatingthe gel electrolyte and the thickness ratio A/B of the total filmthickness A of the positive-electrode active material with respect tothe total film thickness B of the negative-electrode active materiallayer are obtained. Thus, according to the present invention, a solidelectrolyte battery can be provided which is able to raise the energydensity thereof without deterioration in the discharge loadcharacteristics of the battery.

Although the invention has been described in its preferred form andstructure with a certain degree of particularity, it is understood thatthe present disclosure of the preferred form can be changed in thedetails of construction and in the combination and arrangement of partswithout departing from the spirit and the scope of the invention ashereinafter claimed.

What is claimed is:
 1. A solid electrolyte battery comprising: a woundelectrode comprising a positive electrode comprising an elongatedpositive-electrode collector having two sides on whichpositive-electrode active material layers are formed, a negativeelectrode comprising an elongated negative-electrode collector havingtwo sides on which negative-electrode active material layers are formed,and a solid electrolyte layer comprising a gel electrolyte comprising acopolymer of polyvinylidene fluoride and hexafluoropolypropylene,wherein said hexafluoropolypropylene is copolymerized at a ratio lowerthan 8 wt % of said polyvinylidene fluoride and wherein said solidelectrolyte layer is formed between said positive electrode and saidnegative electrode such that said positive electrode and said negativeelectrode are laminated and wound; and wherein when the total thicknessof a pair of said positive-electrode active material layers formed onthe two sides of said collector for said positive electrode is totalfilm thickness A and the total thickness of a pair of saidnegative-electrode active material layers formed on the two sides ofsaid collector for said negative electrode is total thickness B, thetotal film thickness A of said positive-electrode active material layerssatisfies a range from 60 μm to 150 μm, and ratio A/B of the total filmthickness A of said positive-electrode active material layers withrespect to the total thickness B of said negative-electrode activematerial layers satisfies a range from 0.5 to 1.2.
 2. A solidelectrolyte battery according to claim 1, wherein saidhexafluoropolypropylene is block-copolymerized at a ratio fromapproximately 3 wt % to approximately 7.5 wt % of said polyvinylidenefluoride.
 3. A solid electrolyte battery according to claim 1, whereinsaid positive-electrode active material is prepared by using compositelithium oxide mainly composed of Li_(x)MO₂(where M is one or more typesof transition metal, preferably Co, Ni or Mn and x varies depending on astate of charging/discharging of said battery and satisfies0.05≦×≦1.12).
 4. A solid electrolyte battery according to claim 1,wherein said negative-electrode active material is a material which iscapable of doping/dedoping lithium.
 5. A solid electrolyte batteryaccording to claim 4, wherein said material which is capable ofdoping/dedoping lithium is at least one material selected from a groupconsisting of graphite, a non-graphitizable carbon material and agraphitizable carbon material.
 6. A solid electrolyte battery accordingto claim 1, wherein said wound electrode is encapsulated by a laminatedfilms, and a lead of said positive electrode and a lead of said negativeelectrode connected to said wound electrode are drawn out to the outsideportion of said laminated films.
 7. A solid electrolyte batterycomprising: a wound electrode comprising a positive electrode comprisingan elongated positive-electrode collector having two sides on whichpositive-electrode active material layers are formed, a negativeelectrode comprising an elongated negative-electrode collector havingtwo sides on which negative-electrode active material layers are formed,and a solid electrolyte layer comprising a gel electrolyte comprising acopolymer of polyvinylidene fluoride and hexafluoropolypropylene,wherein said hexafluoropolypropylene is copolymerized at a ratio lowerthan 8 wt % of said polyvinylidene fluoride and wherein said solidelectrolyte layer is formed between said positive electrode and saidnegative electrode such that said positive electrode and said negativeelectrode are laminated and wound through a separator; and wherein whenthe total thickness of a pair of said positive-electrode active materiallayers formed on the two sides of said collector for said positiveelectrode is total film thickness A and the total thickness of a pair ofsaid negative-electrode active material layers formed on the two sidesof said collector for said negative electrode is total thickness B, thetotal film thickness A of said positive-electrode active material layerssatisfies a range from 60 μm to 150 μm, and ratio A/B of the total filmthickness A of said positive-electrode active material layers withrespect to the total thickness B of said negative-electrode activematerial layers satisfies a range from 0.5 to 1.2.
 8. A solidelectrolyte battery according to claim 7, wherein saidhexafluoropolypropylene is block-copolymerized at a ratio fromapproximately 3 wt % to approximately 7.5 wt % of said polyvinylidenefluoride.
 9. A solid electrolyte battery according to claim 7, whereinsaid positive-electrode active material is prepared by using compositelithium oxide mainly composed of Li_(x)MO₂(where M is one or more typesof transition metal, preferably Co, Ni or Mn and x varies depending on astate of charging/discharging of said battery and satisfies0.05≦×≦1.12).
 10. A solid electrolyte battery according to claim 7,wherein said negative-electrode active material is a material which iscapable of doping/dedoping lithium.
 11. A solid electrolyte batteryaccording to claim 10, wherein said material which is capable ofdoping/dedoping lithium is at least one material selected from a groupconsisting of graphite, a non-graphitizable carbon material and agraphitizable carbon material.
 12. A solid electrolyte battery accordingto claim 7, wherein said wound electrode is encapsulated by a laminatedfilms, and a lead of said positive electrode and a lead of said negativeelectrode connected to said wound electrode are drawn out to the outsideportion of said laminated films.